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Nearly 20 million Americans face severe weather risks at week's end

AccuWeather logo AccuWeather 5/28/2020 Alex Sosnowski

The warm and humid conditions in the Northeast could end with a bang as thunderstorms are forecast to erupt and could trigger severe weather on Friday ahead of dramatically cooler air. Nearly 20 million people lie in the zone predicted to experience severe thunderstorms at late week.

a large waterfall over a body of water © Provided by AccuWeather
A mass of clouds with embedded showers and thunderstorms spread over much of the eastern half of the United States on Thursday, May 28, 2020. Former Tropical Storm Bertha is barely distinguishable near the Ohio/Pennsylvania border on this satellite image. Meanwhile, a lack of clouds over the northern Plains marks the leading edge of cooler and drier air. (NOAA / GOES-East)

The warmth this week pushed temperatures in dozens of locations to smash daily record highs, as some cities recorded their highest readings ever for the month of May. Burlington, Vermont, reached 95 F on Wednesday, which set not only a record for the date but also an all-time May record. Montreal and Quebec City also set all-time May records. Scranton, Pennsylvania, tied its all-time May record of 93 on Tuesday.

Temperatures in some coastal areas have been suppressed by cool ocean air, as some places became socked in by low clouds and fog. New York City has yet to reach 80 this week due to the cooling influence of Atlantic waters and fog.

Friday will mark the beginning of the end of the weather pattern more typical of late June and July, but the warm and muggy conditions will set the stage for volatile weather at the end of the week.

A cold front over the Midwest on Thursday will gather momentum and strength as it pushes toward the Northeast on Friday then swings offshore this weekend, and it will act as a trigger for some big thunderstorms. The storms over the Midwest associated with the cool push will carry the risk of localized flash flooding and brief gusty winds into Thursday night.

A tropical air mass has enveloped the Northeast in the wake of Bertha, which made landfall along the South Carolina coast on Wednesday as a tropical storm. Bertha weakened to a tropical rainstorm as it moved over land Wednesday into Thursday. The system sat near the border of Ohio and Pennsylvania on Thursday morning, and the small, fast-moving system is forecast to disperse over southeastern Canada at the end of this week.

As the cooler and less humid air from the North Central states moves in on Friday, it will cause the warm and humid air to be lifted. As that tropical air cools, it will form towering clouds, showers and thunderstorms.

Friday will not be stormy the entire time, but there will be a mosaic of showers and thunderstorms that can bring multiple downpours to some communities. It is possible that it may only actually rain about 10% of the day or less in most areas, but it could be difficult for those looking to do work outdoors or take a long walk without interruptions from a downpour, especially over the Appalachians and eastern Great Lakes region.

The greatest threat for severe thunderstorms is forecast to extend from central West Virginia and northwestern Virginia, northward to central and and northern New York state, as well as southeastern Ontario and southwestern Quebec on Friday.

a close up of a map © Provided by AccuWeather

"The storms are likely to be at their peak intensity from about 1 p.m. to 9 p.m. on Friday," Bill Deger, AccuWeather forecaster, said.


There can also be some small hail with a few of the more intense storms.

"Locally damaging straight-line winds will be the primary threat from these storms," AccuWeather Senior Meteorologist Brett Anderson said. "There will also be brief torrential downpours, but the threat of significant flash flooding will be reduced due to the steady movement of the storms."

There can be a couple of downpours ahead of the severe weather. Pop-up showers and thunderstorms are also possible east of the main severe weather threat zone, including across portions of the mid-Atlantic and New England.

The remnants of these storms will wander toward the mid-Atlantic coast and New England late Friday night and Saturday.

As warm and humid conditions are likely to linger much of the day Saturday, the stage will be set for a new eruption of thunderstorms on near the mid-Atlantic coast and New England. A handful of the storms on Saturday could turn strong or severe.

a close up of a map © Provided by AccuWeather

Farther west, a siege of cooler and less humid air will lower the risk of heavy, gusty thunderstorms across the Appalachians and eastern Great Lakes region on Saturday.

The weather pattern will be ripe for stormy weather across the Great Lakes to the Ohio Valley, central Appalachians and mid-Atlantic next week as heat builds over the middle of the nation. As is often the case during late spring and summer, large complexes of thunderstorms may move around the edge of that dome of heat.

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